新型无氢胺化催化剂PdHx-Pd／C的水合肼还原法制备及形成机制研究

Preparation and Formation Mechanism of New PdH_x-Pd/C Catalyst through Hy drazine-reducing Method under Atmospheric Pressure and H_2-free Conditions

PdHx是Pd/C催化剂中重要的活性物种,在常温无氢的条件下不能稳定存在。在常压无氢条件下,以PdO作前驱体,用水合肼还原法可制备出PdHx含量较高,且能够稳定存在的PdHx-Pd/C催化剂。通过XRD、XPS和TEM等表征方法研究了PdHx和Pd颗粒的微观结构、形貌及化学状态;提出了水合肼还原法生成PdHx的机理。实验结果表明:PdHx颗粒的平均粒径为3.9 nm,PdHx(111)晶面间距比Pd(111)稍大;PdHx生成于水合肼对PdO的还原过程,且其晶粒大小与前驱体PdO的粒度大小及结构不完整性密切相关。将该催化剂应用于无氢条件下胺化法合成2,6-二甲基苯胺的反应中,其催化性能明显优于普通的Pd/C催化剂。

PdHx is an important reactive species for the Pd/C catalyst. Without H2, it can not exist stably at room temperature. This species is usually prepared through reaction of Pd with HE under certain pressure. PdHx-Pd/C catalyst was prepared through hydrazine-reducing method under atmospheric pressure and H2-free conditions. The microstructure, morphology and chemical state of PdHx and Pd particles were investigated by XRD, TEM and XPS characterization methods. The formation mechanism of PdHx particles in the hydrazine-reducing method was pro- posed. Experimental results show that the average particle size of PdHx is 3.9 nm, and the d spacing of PdHx（111） is slightly larger than that of Pd（ll 1）. The PdHx particles derive from the reduction process of PdO by hydrazine. Their particle size is closely related to the particle size and structural imperfection of PdO. The PdHx-Pd/C catalyst demonstrates better catalytic performance than the conventional Pd/C catalyst in the amination reaction to produce 2, 6-dimethylaniline under Hi-free condition.